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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 200px;
            height: 200px;
            background-color: pink;
            /* 边框：solid:实线  dashed:虚线  dotted:点线*/
            /* border: 10px dotted #000; */
             /*  border-方向，指定那个方向需要边框 */
            border-left: 10px solid #000;
        }
    </style>
</head>
<body>
    
    <div>内容</div>
    
</body>
</html>